Integrated semiconductor devices are typically constructed en masse on a wafer of silicon or gallium arsenide. Each device generally takes the form of an integrated circuit (IC) die, which is attached to a leadframe with aluminum, copper or gold wires. The die and leadframe are then encapsulated in a plastic package, which is then recognizable as an IC "chip".
FIG. 1 is a top plan view of a standard dual-inline-package leadframe strip having four interconnected leadframes 11. Leadframe strips with any number of leadframes can be made to order. Leads or pins 12 within a particular leadframe are connected to adjacent pins and a pair of parallel rails 13 by a network of expendable dam bars 14. It will be noted that except at the ends of the leadframe strip, the pins 12 of one leadframe are connected end-to-end to the pins of an adjacent leadframe. Conventional leadframes have a die-mounting paddle 15 that is attached to the rails 13 by expendable tie bars 16. Following the attachment of an IC die on the paddle 15, each die and associated leadframe center section (the center section includes the paddle 15 and the end of each pin which is adjacent paddle 15) are encapsulated in plastic. During the encapsulation process, the dam bars 14 prevent plastic encapsulation compound from seeping between the pins 12. After encapsulation, the pins of individual leadframes are separated from those of adjacent leadframes and from the rails 13 in a trim and form operation. In this operation, the dam bars 14 and tie bars 16 are also stamped out and discarded, and the leads 12 are bent into their final configuration. It will be noted that both rails 13 of a standard leadframe strip are coextensive with the pins 12 of the two leadframes at either end of the strip which are exposed. The pair of rail stubs 17 at each end of the strip afford protection to the exposed pins against bending and breaking, since their much greater width makes them much stiffer than the pins 12.
FIG. 2 is a top plan view of a typical interdigitized dual-inline-package leadframe strip showing six interconnected leadframes (as is the case with standard leadframe strips, the actual number of leadframes on a strip may vary). The pins 21 of adjacent leadframes are intermeshed in order to incorporate a larger number (typically an increase of roughly thirty percent) of leadframes on the strip. The system of dam bars 22 and tie bars 23 is similar to that used with the standard leadframe depicted in FIG. 1. It will be noted for the interdigitized leadframe strip depicted in FIG. 2 that, except at the ends of the leadframe strip where exposed pins 24 are located, the pins of adjacent leadframes are connected at their outer ends to a dam bar which pertains to an adjacent leadframe. Since the individual leadframe strips are cut from a much longer strip without discarding material between individual strips, it was deemed necessary to cut off one rail stub at each end of each interdigitized leadframe strip so that they could remain attached to the adjacent leadframe strips. Locations 25 are the sites of the missing rail stubs. Such a design affords little protection for the exposed pins 24 at either end of the leadframe strip, hence pins become bent and otherwise damaged if not handled with extreme care. Bent pins will require either discarding or repair of the leadframe strip--resulting in either increased material costs or increased labor costs.